Noncemented Hip Replacement using a Conical Screw-In Cup and a Straight Press-Fit Stem. A Six to Eight-Year Clinical and Radiological follow-up Study

Noncemented hip replacement using a conical titanium metal-backed screw-in cup to be implanted with precutting of the threads (TITAN-METAL-BACKED, AlloPro, Baar, Switzerland), in combination with a straight conical press-fit stem (Zweymüller-“hochgezogen”, AlloPro, Baar, Switzerland) was evaluated clinically and radiologically in 64 consecutive primary arthroplasties with an average 7.2 year follow-up. The clinical results compare very favourably with other cementless systems. The Harris hip score revealed an improvement from 45 to 84. The Merle d’Aubigné index showed an increase during the case-control period from 16 to 26. Thigh pain was practically absent except in one patient. A radiographic appearance of bone ingrowth around the acetabular component was found in nearly all cases. Only one cup migrated in a patient with a large cystic lesion in the acetabular roof, which was not grafted, with no other signs of loosening. Additionally this patient had chemotherapy. In all other cases there were no signs of cup migration, significant radiolucency, osteolysis or definite cup loosening. Around the stem, primary cortical contact was mainly located in the distal zones. Radiolucent lines appeared only proximally, with few exceptions, and were, except in four cases, always smaller than 2 mm. They were never circumferential and usually combined with sclerotic lines. Only one stem subsided, but the patient remained asymptomatic. There was a high incidence of proximal bone atrophy, distal cortical thickening and endosteal bone formation, not correlating with radiological loosening or clinical symptoms. Signs of femoral osteolysis were absent. No patient had to be revised.